One of the most common causes of misfires from reloaded ammo is that the primer is not seated in the pocket far enough. When the firing pin hits the primer cup the energy from the firing pin is directed to pushing the primer into the pocket to it's "proper" position. The pin's energy is used up doing this and the pin will not "dent" the primer enough to ignite it. This is why it will sometimes go off if a second attempt to fire it is tried.

Reloaders (myself included, as I have had this happen several times with all makes of primers and primer tools) must pay attention to this aspect of reloading.